Thakur Siddharth, Dasmahapatra Ashok Kumar, Bandyopadhyay Dipankar
Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati, Assam 781039, India.
Centre for Nanotechnology, Indian Institute of Technology Guwahati, Guwahati, Assam 781039, India.
ACS Appl Mater Interfaces. 2021 Dec 22;13(50):60697-60712. doi: 10.1021/acsami.1c21811. Epub 2021 Dec 7.
A single-step self-organized pathway is harnessed to generate large-area and high-density liquid-crystal (LC) microdroplets via rapid spreading of an LC-laden volatile liquid film on an aqueous surfactant bath. The surfactant loading on the water bath and LC loading in the solvent fluid help in tuning the size, periodicity, and ordering of LC microdroplets. Remarkably, the experiments reveal a transition from a spinodal to heterogeneous nucleation pathway of dewetting when the surfactant loading is modulated from below to beyond the critical micellar concentration in the aqueous phase. In the process, a host of unprecedented drop formation modes, such as dewetting and contact-line instability, random ejection, and "fire cracker" toroid splitting, have been uncovered. Subsequently, the LC microdroplets on the air-water interface are employed as photomasks suitable for soft-photolithography applications. Such masks help in the decoration of a host of mesoscale three-dimensional features on the films of photoresists when photons are guided through the LC droplets. In such a scenario, phase transition of LC droplets under solvent vapor annealing is employed to control the movement of photons through drops and subsequently modulate the light exposure on the photoresist surface. Such a simple soft-photolithography setup leads to an array of flattened droplets on a positive resist, while donut features are observed on the negative tone. Remarkably, the orientation of nematogens within 4-cyano-4'-pentylbiphenyl droplets and at the three-phase contact-line provides additional handles in controlling the transmission of photons, which facilitates such a unique pattern formation. A number of low-cost and simple strategies are also discussed to order such soft-photolithography patterns. Importantly, with a minor modification to the same experimental setup, we could also measure the variation in the order parameter of the LC droplet during its phase transitions from the nematic to isotropic state.
通过在水性表面活性剂浴上快速铺展载有液晶（LC）的挥发性液体薄膜，利用单步自组织途径生成大面积、高密度的液晶微滴。水浴上的表面活性剂负载量和溶剂流体中的液晶负载量有助于调节液晶微滴的尺寸、周期性和有序性。值得注意的是，实验表明，当表面活性剂负载量从低于临界胶束浓度调制到超过水相中的临界胶束浓度时，会发生从旋节线到异质成核的去湿转变。在此过程中，发现了许多前所未有的液滴形成模式，如去湿和接触线不稳定性、随机喷射以及“鞭炮”环形分裂。随后，气 - 水界面上的液晶微滴被用作适用于软光刻应用的光掩模。当光子穿过液晶微滴时，这种掩模有助于在光刻胶膜上装饰许多中尺度三维特征。在这种情况下，利用溶剂蒸汽退火下液晶微滴的相变来控制光子通过微滴的运动，进而调节光刻胶表面的曝光。这种简单的软光刻装置在正性光刻胶上形成一系列扁平液滴阵列，而在负性光刻胶上观察到甜甜圈特征。值得注意的是，4 - 氰基 - 4'- 戊基联苯微滴内以及三相接触线上的向列相分子取向为控制光子传输提供了额外手段，这有助于形成这种独特的图案。还讨论了一些低成本且简单的策略来排列这种软光刻图案。重要的是，对相同实验装置进行微小修改后，我们还可以测量液晶微滴从向列相到各向同性相转变过程中序参量的变化。
